The majority of minors: on the identity and function of rare soil bacteria

Most bacterial taxa in soil are low abundant or rare. Usually, rare species are not expected to contribute substantially to ecosystem functioning, however, recent studies suggest that rare bacteria can play a crucial role in soil, for example by possessing distinct traits and acting as keystone species in biogeochemical cycles, by providing an insurance function under changing environmental conditions, or through interactions with other organisms such as plants and plant enemies. Our aim is to identify rare bacterial taxa in soil and investigate their contribution to ecosystem functioning. We use a number of approaches: First we identify bacterial taxa that are constantly rare or exhibit fluctuating abundances by mining sequence databases. Cultivation-based approaches employing flow cell sorting and nutrient-poor media will be used to investigate specific characteristics of permanently rare bacteria, such as cell size and growth rate and the ability to degrade certain substrates. Then, we test their putative role in the insurance of ecosystem functions by monitoring the abundance of selected rare taxa using qPCR under disturbance regimes such as are likely to occur under human influence. Finally we will assess the effects of the loss of rare bacteria on plant biomass production and plant community evenness. Ultimately changes in the induction of systemic plant defences as the result of loss of rare bacterial taxa will be investigated as one mechanism by which rare bacteria might affect plant performance. The combination of approaches will enable us to determine the roles of a selection of rare bacterial taxa in ecosystems. We will test which factors may be influenced by rare taxa: the possession of distinct traits, insuring ecosystem functions under environmental change or affecting plant defences. This approach will enable us to predict consequences of losing rare soil bacteria from ecosystems.